Orthopedics is a medical specialty concerned with the correction of deformities or functional impairments of the skeletal system, especially the extremities and the spine, and associated structures, such as muscles and ligaments. Some orthopedic surgical procedures require surgeons to secure a device to one or more bones of a patient. For example, in some procedures, the surgeon may span and secure one or more bones, or pieces of a single bone, using a bone plate and one or more fasteners, such as screws. Other bone-related surgical procedures, however, may not require a bone plate and may instead solely rely on the use of one or more screws (e.g., securing a transplanted tendon).
In such bone-related surgical procedures, before an implant or plate, or simply the screw itself, can be attached to bone, an opening is typically drilled into the bone to accommodate the screw. With a hole in place, the surgeon can more easily select a screw of the appropriate length. However, selecting a screw of appropriate length is critical. For example, if the selected screw is too long, the distal end of the screw may pass through the end of the drilled hole and cause damage to the bone and/or protrude entirely through the bone, which can have deleterious effects, such as damage to surrounding tissue and/or pain and discomfort, or more serious complications, for the patient. For example, in some instances, the bone may abut against soft tissues that may be harmed if the screw is too long and may result in irritation of or damage to the soft parts. Additionally, a screw that protrudes through the bone may be tactilely felt by the patient, may prevent soft tissues (e.g., tendons, ligaments, or muscles) from moving over the bone surface as intended, or may even pierce the skin, which can lead to serious infection and complications.
The selection of an appropriate length screw is particularly important in spinal fixation procedures, such as lumbar sacral fusion and the correction of spinal deformities such as scoliotic curves. As an example, a screw mounted in the pedicle portion of the human spine should not extend to a point where the screw contacts the spinal cord itself, an event that can cause irreparable nervous system damage including paralysis. Accordingly, the determination of a length of the hole is important for choosing the appropriate length screw.
During drilling, the surgeon is typically capable of recognizing the resistance on the drill in order to determine when the drill has penetrated through the bone. Because the simple act of drilling does not provide an exact measurement of the depth of the bone itself, a depth gauge is commonly employed for directly measuring the depth of the hole from the top, drilling side to the bottom, opposite side of the hole.
Currently, many designs are known and utilized for measuring the depth of a hole or bore in a portion of a bone. Generally speaking, these designs utilize a central probe member having a barb at a distal end, and a sleeve or channel member. The probe member is inserted into the pilot hole while the surgeon attempts to find the surface with the barb. More specifically, the probe member is inserted to a depth greater than the depth of the pilot hole so that the barb is beyond the opposite side, at which point the surgeon finds the surface by hooking the barb to the opposite side.
The probe member is received in the sleeve or channel member and may reciprocate relative thereto. The channel member has graduated markings along a portion of its length, typically in inches and/or millimeters. A marker is laterally secured to the probe member such that, as the probe member shifts relative to the channel member, the marker indicates the relative shift between the probe member and the channel member. Accordingly, once the probe member has been secured to the opposite side of the bone, the channel member is shifted relative to the probe member and toward the bone until the channel member abuts the surface of the bone. The depth gauge is then read by examining graduated markings indicated by the probe member marker.
A number of problems are experienced with this depth gauge. As an initial point, the components are typically made with surgical-grade stainless steel, and the graduated markings are embossed therein. Therefore, the brightness of the operating room lights on the highly reflective surface can make the markings difficult to read. The markings are commonly in small increments, such as millimeters, and surgeons often have trouble differentiating between the markings, or noting partial increments. Reading these gauges, then, often requires carefully holding the depth gauge as the reading is taken, and a surgeon's effort to closely examine the reading may result in a loss of securement or purchase of the barb on the bone, thus necessitating a re-measurement and a loss of time.
Furthermore, proper reading of the markings requires a surgeon's eyes to be properly aligned with the markings. That is, a proper view of the measurement requires the surgeon to view the gauge from a lateral point of view so that the view of the probe marker aligned with the graduated markings is proper not distorted by the surgeon's elevated, standing perspective. Therefore, it is often necessary for the surgeon to bend over while using these gauges to view an accurate reading. If the depth gauge is tilted in order to make the reading, the sleeve will shift relative to the probe, thus making the measurement inaccurate and possibly causing the barb to become unsecured, as described above. In addition, removal of the depth gauge often causes the measurement to be lost. As the bone is essentially clamped, by light pressure, between the distal end of the channel member and the distal barb of the probe member, it is often necessary to retract the channel member from the bone surface in order to extract the probe from the pilot hole.